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14. CHAIN RULE
_IMPORTANT FACTS AND FORMULAE
1. Direct Proportion:
Two quantities are said to be directly proportional, if on the increase (or
decrease) of the one, the other increases (or decreases) to the same
Ex. 1. Cost is directly proportional to the number of articles.
(More Articles, More Cost)
Ex. 2. Work done is directly proportional to the number of men working on it
(More Men, More Work)
2. Indirect Proportion:
Two quantities are said to be indirectly proportional,if on the increase of the
one, the other decreases to the same extent and viceversa.
Ex. 1. The time taken by a car in covering a certain distance is inversely proportional to the speed of
the car.
(More speed, Less is the time taken to cover a distance)
Ex. 2. Time taken to finish a work is inversely proportional to the num of persons working at it.
(More persons, Less is the time taken to finish a job)
Remark:
In solving questions by chain rule, we compare every item with the term to be found out.
SOL VED EXAMPLES
Ex. 1. If 15 toys cost Rs, 234, what do 35 toys cost?
Sol.
Let the required cost be Rs. x. Then,
More toys, More cost
(Direct Proportion)
.
15 : 35 : : 234 : x
ó
(15 x x) = (35 x 234)
ó
x=(35 X 234)/15 =546
Hence, the cost of 35 toys is Rs. 546.
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 Spring '11
 vinh

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